A New South Wales man accused of stabbing his grandmother to death and leaving his grandfather critically injured has apologised in court.

Murray Deakin, 20, is accused of carrying out the attack at the couple's Bega home on Friday afternoon before stealing their car and then carjacking another vehicle during his getaway.

Murray Deakin is accused of stabbing his grandparents. (Supplied) (9NEWS)Police at the scene on Friday. (9NEWS) (Nine)

He allegedly bashed that car's 55-year-old driver with a hammer.

The man was flown to St George Hospital where he died this afternoon.

Mr Deakin's 71-year-old grandfather managed to escape onto the street outside and flag down a passing driver for help, however his 69-year-old wife later died at South East Regional Hospital.

Mr Deakin's grandmother died following the alleged attack. (9NEWS) (Nine)

The Daily Telegraph has reported the grandfather, who was flown to Canberra Hospital, told police his grandson was schizophrenic.

However Inspector Sue Charman-Horton wouldn't be drawn on the possibility mental health issues or drugs drove the attack, only going so far as to describe the man as "unwell" and saying he "certainly needed to be looked at".